The present invention relates to a printing apparatus for performing printing using a printhead with a plurality of printing elements, a control method therefor, and a computer-readable memory.
Note that the present invention is applicable not only to a general printing apparatus but also to a copying machine, a facsimile apparatus having a communication system, a word processor having a printing unit, and an industrial printing apparatus combined with various processors.
Serial-scan printing apparatuses for printing data while scanning a printing medium with a printhead are applied to formation of various images. Particularly, inkjet printing apparatuses are rapidly being spread because of higher resolution, advanced color printing, and higher image quality in recent years.
Such a printing apparatus prints an image at a higher resolution by decreasing the ink discharge amount per dot while increasing the integration density of nozzles for discharging ink droplets. To realize an image quality equivalent to a silver halide photograph, various techniques have been developed such that printing is done simultaneously using four basic color inks (cyan, magenta, yellow, and black), and light inks prepared by decreasing the ink concentrations of these basic color inks. As the ink concentrations are related to image density, the ink concentrations will also be hereinafter referred to as ink densities. The printing speed, which may decrease for higher image quality, can be increased by increasing the number of printing elements and the driving frequency, and using a printing technique such as two-way printing of performing printing in reciprocal scans of a printhead.
In a printhead containing many printing elements, a defective printing element (to be also referred to as a defective channel hereinafter) is generated over time in accordance with the use frequency. As the number of printing elements aligned at a high integration density increases, the probability of generating defective printing elements in manufacturing a head also increases. If an integrated structure for a plurality of colors is adopted to prevent color misregistration and improve the operability, this probability further increases. Although most printing elements are nondefective, even one defective printing element degrades the image quality. Importantly, such a printhead cannot be used for the recently required application of printing photographic images.
There have already been proposed many methods in response, including various defective printing element detection methods, and recovery methods or printing methods corresponding to the detection results. Such methods in printing when a defective printing element exists are disclosed in Japanese Patent Laid-Open Nos. 5-309874, 61-123545, 11-988, 11-77986, and 10-258526.
Japanese Patent Laid-Open No. 5-309874 discloses a method of setting the number of multipass printing operations in accordance with image data to be printed, the presence/absence of a defective printing element, and the type of image because image degradation by a defective printing element is reduced by multipass printing of printing an image while scanning a predetermined region of the image by a printhead a plurality of number of times.
However, even if the number of scan operations (passes) in multipass printing is increased, the influence of a defective printing element on an image stands out as a stripe on a high-quality photographic image, an application which has been in demand more and more in recent years. To obtain a higher image quality, the number of passes must be greatly increased. From the two points, the invention discloses in the above reference cannot be practically used.
Japanese Patent Laid-Open No. 61-123545 discloses a method of printing image data of a defective channel by a nondefective channel mainly in 1-pass printing of a predetermined region of an image by one scanning of a printhead. When a carriage prints data to the right, normal printing is done. When the carriage moves to the left, a sheet is fed by an integral multiple of one pixel for the purpose of complementary printing of a pixel by a nondefective printing element which cannot be printed by a defective printing element. That is, a defective channel is complemented by a nondefective channel. This method completely complements image data, but assumes 1-pass printing. Thus, the method cannot cope with a color mode in which a high-quality photographic image is printed, which is an object of the present invention. The original printing method is 1-pass printing, but alternate printing is substantially 2-pass printing in which the throughput is low.
Japanese Patent Laid-Open No. 11-77986 discloses a method of counting the use frequency of a complementary nozzle, and when the total use frequency reaches a predetermined value, sequentially switching complementary nozzles in consideration of the service life of each complementary nozzle on the complementary printing side. Similar to Japanese Patent Laid-Open No. 61-123545, this method assumes 1-pass printing and cannot cope with a color mode in which a high-quality photographic image is printed, which is an object of the present invention.
Japanese Patent Laid-Open No. 11-988 discloses an arrangement in which n/m printing elements prepared by dividing n printing elements by m (the divisor of the number of nozzles) are set as first printing elements used for a normal printing scan. Other n(mxe2x88x921)/m printing elements are set as second printing elements not used for the normal printing scan, and the printing operation is effected using a second printing element as an alternate printing element only when a first printing element is defective. This arrangement basically assumes a multipass printing method of completing an image by repeating the printing scan and sheet feeding m times for a single image region. This method can complement an image without decreasing the throughput. However, this printing method (generally called interlaced printing) is one in which an image of one line in the carriage scan direction is completed by one printing scan with one printing element.
Japanese Patent Laid-Open No. 10-258526 assumes multipass printing, similar to Japanese Patent Laid-Open No. 5-309874, and discloses a method of complementing omitted data of one nozzle by another nozzle. After a standard mask is obtained prior to printing, a defective nozzle is specified, and an alternate exchange nozzle is selected in accordance with the position of the defective nozzle. Printing data of the defective nozzle is erased from its mask, and added to the mask of the exchange nozzle. This method can print an image without decreasing the throughput, even in a color mode in which a high-quality photographic image is printed, which is an object of the present invention.
As printers are becoming more for personal use and smaller in size, cartridge-type printheads or ink tanks are becoming popular. Printhead or ink tanks are individually different in their manufacture or practical use. This occurs due to different driving methods of discharging proper amounts of ink droplets, or due to concerns about the remaining ink amount in an ink tank which has already been used by another main body. Information about the cartridge characteristics is effectively stored not in a printing apparatus, but in each printhead or ink tank. This is because a plurality of cartridges are mounted/dismounted on/from a plurality of main bodies. From this, Japanese Patent Laid-Open No. 6-320732 discloses that an EEPROM is mounted on a board constituting a printhead, the EEPROM stores information about the characteristics of the printhead such as printhead driving conditions or density unevenness correction data, or information about the printing history such as the number of printed sheets or the number of discharge operations, and driving conditions and the like are updated in accordance with the information. In practice, many printing apparatuses employ this arrangement.
However, each conventional method in printing when a defective printing element exists suffers a problem such that either the complement is imperfect, the throughput decreases, or the complementary load concentrates on one nozzle. Even in the complementing method disclosed in Japanese Patent Laid-Open No. 10-258526, which assumes multipass printing, the number of complementary candidates increases, but either the discharge load is double the normal discharge load or continuous driving is concentrated on one nozzle in actual printing. For this reason, this method is not the most preferable complementing method in terms of the service lives of the nozzle and printhead.
The present invention has been made to overcome the conventional drawbacks, and has as its object to provide a printing apparatus for realizing stable, efficient printing, a control method therefor, and a computer-readable memory.
A printing apparatus according to the present invention for achieving the above object has the following arrangement. A printing apparatus for performing printing using a printhead with a plurality of printing elements is characterized by comprising storage means for storing at least defective printing element information about a defective printing element among the plurality of printing elements, determination means for determining a complementary printing element for masking printing data corresponding to the defective printing element indicated by the defective printing element information and complementarily printing the printing data corresponding to the defective printing element, and printing means for printing the printing data of the defective printing element using the complementary printing element determined by the determination means.
A control method for a printing apparatus according to the present invention for achieving the above object has the following steps. A control method for a printing apparatus for performing printing using a printhead with a plurality of printing elements is characterized by comprising the determination step of referring to a storage medium which stores at least defective printing element information about a defective printing element among the plurality of printing elements, and determining a complementary printing element for masking printing data corresponding to the defective printing element indicated by the defective printing element information and complementarily printing the printing data corresponding to the defective printing element, and the printing step of printing the printing data of the defective printing element using the complementary printing element determined in the determination step.
A computer-readable memory according to the present invention for achieving the above object has the following program codes. A computer-readable memory storing program codes of control of a printing apparatus for performing printing using a printhead with a plurality of printing elements is characterized by comprising a program code of the determination step of referring to a storage medium which stores at least defective printing element information about a defective printing element among the plurality of printing elements, and determining a complementary printing element for masking printing data corresponding to the defective printing element indicated by the defective printing element information and complementarily printing the printing data corresponding to the defective printing element, and a program code of the printing step of printing the printing data of the defective printing element using the complementary printing element determined in the determination step.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.